Method of separating sulphur dioxide and chlorine from mixtures



Patented Febr8 f UNITED STATESIQUPATENT. omega 2,840,981 I METHOD OF 'SEPABATING SULPHUR DI- OXIDEAND CHLORINE FROM BIIXTUBIES Arthur W. Hixson, vIieonia, N. -J.. and Ralph Miller, New York. N. Y., assignorsto'lhe Chem- 1 ical Foundation, Incorporated, a corporation of Dela-ware, as trustee I No Drawing. Application December 11 1941,

' Serial No. 422,592

a cum; 101. zs-rm This invention relates to a methodoi separatseparation methods involved either low temlng sulphur dioxide and chlorine from mixtures perature or high pressure i'oriiqueiaction; this thereof. is rather undersir'able in that it requires caretu As disclosed in copending application Serial control and expensive equipment. c No. 263,190, filed March 21, 1939, it has been 5 As aresult of intensive experimentation ithas found that chlorine and sodium sulphate may be been found that the separation of sulphur diox; produced from sodium chloride and sulphur by ide and chlorineirom gaseous mixtures thereof v 1 eii'ective methods. As therein disclosed this may be eflectuated in simple and efllcient manmay be accomplished in one method by convertner. '1

ing sulphur-to sulphur trioxide and contacting The invention comprehends the concept of this, free from oxygen, with. sodium chloride toseparating sulphur dioxide and chlorine by se-v i'orm sodium chlorosulphonate which is then lectively reacting the sulphur dioxide with a mathermally decomposed to form sodium sulphate, terial with which it iorms a solid addition'comchlorine and sulphur dioxide. In the complete pound and whichmaterial does not react with operation the chlorine and sulphur dioxide are chlorine. The new method of separation may 'separated, the sulphur dioxide oxidizedtosulbe carried out under relatively-wide variations phur trioxide which is recycled for reaction with oftemperature and pressure thus insuring its additionalquantities of salt. In a more specific adaptionto optimum conditions. sense the invention comprises the steps of oxi-. It has been discovered that zirconium tetra-' dizing sulphur tosulphur dioxide. converting the 0 chloride is well suited to effect the described I latter to sulphur trioxide; cooling the sulphur separation. This product, as is known, is a trioxide andadsorblng it inoleum; heating the white powder which is quite hygroscopic. It has oleurn to evolve sulphur trioxide; contactingthe been ascertained that zirconium I tetrachloride evolved sulphur trloxide with sodium chloride to reacts with sulphur dioxide, in the presence of ram sodium chlorosulphonate, then thermally gaseous chlorine to form a direct solid addition decomposing the sodium chlorosulphonate to compound. The addition reaction takesplace at formagsseous mixture of sulphur dioxide and low temperatures of the order or 0 C. to about chlorine and solid sodium sulphate. In the 1 10 C. for lower. The addition compound is priorapplication the gaseous inixture was sepathermally unstable, decomposing slowly at room rated into its components by certain described temperatures and completely at 100 C. Formethods. In the present invention this separatuitously zirconium does not liqueiy at elevated tion of sulphur dioxide and chlorineis eflected temperatures but sublimes at about 300 C; The

very simply by utilizing a reagent which forms addition reaction described is exothermic hence an addition compound with sulphur dioxide. 7 in carrying out the SOs-C12 separation it is de In another method choiorsulphonic acid is ie- 3;, sirable to cool or refrigerate the reaction so as to acted with sodium chloride to form sodium chlomaintain the temperature at the low value fav- 'ride to form sodium chlorosulphonate and'gase-fi orable to the formation of the addition comous hydrogen chloride. The chlorosulphonate is pound.

then thermally decomposed to form sodium sul- It will be appreciated from the foregoing that phate, sulphur dioxide and chlorine. Here 1 zirconium tetrachloride is well suited for the sep-= again the sulphur dioxide andfiifchlorine aresepeoration of sulphur dioxide from chlorine, and

' rate the phur dioxide is O'Xidlzedto sulphur" while this separation may be effected'in liquid trioxide and reacted with hydrogen chloride to 'phaseitis obviously preferable to carry out the iorm chlorosulphonio acid which is then used to operation in the gaseous-phase. In carrying out 7 m t i h further amounts of salt. the invention an equimolecular mixture of sul- According t0 8 thod sulphur trloxide phur dioxide and chlorine produced by the re- -and sodium chloride are reactedat elevated actions described hereinbeicre is passed through mm s directly 10ml Sodium Sulphate suitable cooling apparatus to reduce ,its -temnd a im 0! c -ml sulphur id 'perature down to the order of 0 c. to -1o 'c; Thesulphur dioxide a d h o are then l so or below. The cooled gas is then passed through wtrlordde which is recycled in the process. chloride. Preferably the tetrachloride ,is dis- In each'of these methods a step or major imtributedon plates or 'in inert material so as to portance is the separation of chlorine and sui-i permitjree passage of the gaseous mixture:

rated; thesulphur dioxide is oxidized to sulphur a chamber containing the solid zirconium tetra phur dioxide. In the earlier application the II- therethrough underconditions insuring .maximum contact of the gas with the solid absorbent material; The contact chamber containing the tetrachloride may be provided with cooling coils or other cooling means to absorb the exothermic heat of the reaction and maintain the optimum low temperature.

In the complete operative process it is desirable to utilize the tetrachloride to absorb the sulphur dioxide and to regenerate the tetrachloride I for reuse. This may be accomplished by employing two or more towers through which the gas to be'treated may alternately be passed. The cooled gaseous mixture, to be separated may be passed through one tower packed with zirconium tetrachloride in the manner described. In addition to the cooling means each tower maybe provided with a heating means available for the decomposition of the addition compound. The aas is flowed through the first tower at such a rate that all the sulphur dioxide in the entering mixture reacts with zirconium tetrachloride, The chlorine, freed from sulphur dioxide is withdrawn from the tower and passed to' a receiver.

When the zirconium tetrachloride in one tower is completely reacted and exhausted the flow of the enteringgas is then diverted to a second tower of the battery in which the sulphur dioxide is reacted with the tetrachloride.

2. A method of separating sulphur dioxide and chlorine from a mixture thereof which comprises contacting the mixture at low temperature with zirconium tetrachloride to form a non-gaseous addition compound of the zirconium tetrachloride and sulphur dioxide, separating chlorine and the addition compoimd and heating the addition gaseous mixture to preferentially abstract the sulphur dioxide from the mixture by forming an addition compound of sulphur dioxide and the zirconium tetrachloride and continuously removing chlorine substantially free from sulphur dioxide.

4. A method of separating sulphur dioxide and chlorine from a gaseous mixture thereof which comprises, continuously contacting zirconium tetrachloride with a flowing stream of the gaseous mixture at a temperature below 0 C. to preferentially abstract the sulphur dioxide from the mixture by forming an addition compound of sulphur. dioxide and the zirconium tetrachloride and Pure sulphur dioxide may be passed through the first tower to sweep out any residual chlorine andthis gas mixture may be passed to the second tower for fractionation therein.

When the first tower has been cleared of chicline the addition compound is treated in situ receiver and may again be utilized in the process by oxidation to sulphur trioxide which may be reacted with sodium chloride by any of the methods hereinbefore described. After driving oil! the 80: from the addition compound the first tower may be put back on stream. By this method of alternating the entering gas stream between two or more towers a substantially continuous operation may be carried out. 7

Of course it will be appreciated that if desired the spent tetrachloride, i. e., the addition compound maybe passed to a separate unit for reeneration therein.

It is found in actual operations about 233 pounds of zirconium tetrachloride will combine scribed process is given as illustrative of the utilization of materials having the characteristics of zirconium tetrachloride for the described separation. d

We claim:

l. A'method'of separating sulphur dioxide and continuously removing chlorine substantially ride continuously removing chlorine substantially chlorine from a gaseous mixture of these components which comprises contacting the low temperature mixture with zirconium tetrachloride under conditions regulated to eilect the formafree from sulphur dioxide, thermally decomposing the addition compound to form sulphur dioxide and zirconium tetrachloride and reemplaying the regenerated zirconium tetrachloride in the process.

= -6. The process of producing chlorine and sodiv with sodium chloride to form sodium chlorosulphonate; thermally decomposing the sodium chlorosulphonate to form a gaseous mixture of chlorine, arid sulphur dioxide and solid sodium sulphate, separating the solid sodium sulphate from the gaseous mixture;.contacting the gaseous mixture with zirconium tetrachloride under conditions regulated to form an addition compound of sulphur dioxide and the tetrachloride; separating gaseous chlorine from the solid addition compound; thermally decomposing the solid addition compound to form sulphur dioxide and regenerated zirconium tetrachloride; oxidizing the recovered sulphur dioxide to sulphur trioxide for recycling in the process and reemploying the regenerated zirconium tetrachloride for separation of sulphur dioxide from its mixture with chlorine.

7. A method of separating sulphur dioxide and chlorine from a'gaseous. mixture of these components which comprises coolingthe mixture to a temperature of the order of from appr0xi mately 0 C; to 10- C., contacting the mixture with zirconium tetrachloride to effect the formation of an addition compound of the tetrachloride and sulphur dioxide and recovering chlorine substantially free from sulphur dioxide. I

8. A method of separating sulphur dioxide and chlorine from a gaseous mixture of these components which comprises contacting the mixture I with zirconium tetrachloride while maintaining 'the mixture at a temperature below about 0 C.

to efiect the formation of an addition compound of the tetrachloride and sulphur dioxide and withdrawing the unreacted chlorine substantially free from sulphur dioxide.

9. In the method of producing sodium sulphate and chlorine from sodium chloride that improvement which comprises, reacting sulphur trioxide with sodium chloride under conditions regulated to form solid sodium sulphate and a gaseous mixture of chlorine and sulphur dioxide in substantially equimolecular proportions, removing the gaseous mixture from the solid products of the reaction, contacting the gaseous mixture with zirconium tetrachloride to form a solid addition compound of the tetrachloride and the sulphur dioxide thermally decomposing the compound to form sulphur dioxide and regenerated zirconium 

